Condition duration and damage
I would say duration would be better because an enemy player can do more overall damage to himself if he keeps spamming attacks while confused. There is the chance for them to cleanse it off or they will have to sit around and not attack for a longer period to avoid damage.
depends on pvp or pve
in pve mobs attack so slow that you’d really need duration to get more than maybe 2 hits from it off, pvp you want damage to maximize the burst damage before they get removed.
You have to make the choice yourself, both have good and bad points, you can get the raw damage quicker with condition damage and reduce the chance of the condition being stripped by the player or you can try maximise your damage overtime but risk players stripping your condition stacks off.
As Dasorine said, PvE is hands-down duration; condition removal is rare on mobs and slow attack cycles make it a must.
In PvP I’d say it depends on how you’re applying it. If you prefer a burstier confusion and tend to load high stacks in batches, go for damage – condition removal will undermine duration gains.
If you’re running a more sustained application (generally less concerned about the damage, more about control), then you should probably focus on duration, since most opponents can only pop condition removal so often, so after the first couple of rounds are dropped you can start to lean on them for longer stretches.
In a big group I’d say damage over duration regardless, since enemies will either die very quickly (small group) or have condition removal constantly firing (big group); either way you want to squeeze in what you can quickly.
as for pve in fact if you are playing a mesmer (the one with easiest access to lots of confusion for sure) you have to remember that your illusions (clones and phatasms) DO NOT get any effect from con duration, where they do get the benefit of your con damage. so if you apply a lot of conditions from clones you want to go for dmg nor duration
Somebody on the Mesmer forums posted up a spreadsheet earlier this year showing that a 10% increase in Confusion Duration is equivalent to about 300 Condition Damage. This is based on WvW numbers using an overall average 1.4 attacks per second.